main(List<String> args) {
  // while语句
  // while do-while
  int count = 0;

  while (count < 5) {
    print(count++);
  }

  print('--------$count---------');

  do {
    print(count--);
  } while (count > 0);

  print('------------------');

  count = 5;

  do {
    print(count--);
  } while (count > 0 && count < 4);
}
